You have to remember that even if she was to be a teapot, it doesn't mean that you'll have a 15 lb yorkie with the body frame of a 6 lb one. It's proportionate, you'll have a 15 lb dog with the body frame of a 15 lb dog. The muscles will be adequate for the body type. Energy level does change with personality. Mellow dogs are much calmer, like my dog. that doesn't mean he doesn't have the capability of running around like a mad man. He just chooses when and where.
